1. Field of the Invention
The present invention relates in general to a control apparatus for a vehicular power transmitting system, and more particularly to a control apparatus for a vehicular power transmitting system including an electrically controlled differential portion which includes an electric motor and an operating speed of which is controlled by the electric motor, and a switching portion which constitutes a part of a power transmitting path between the electrically controlled differential portion and a drive wheel of a vehicle and which is operable to switch the power transmitting path between a power transmitting state and a power cut-off state.
2. Discussion of Prior Art
There is known a vehicular drive system including (a) a drive power source in the form of an engine, (b) an electrically controlled differential portion which has a differential mechanism and a first electric motor connected to a rotary element of the differential mechanism and which is operable to control a differential state between rotating speeds of its input shaft connected to the engine and a rotating speed of its output shaft by controlling an operating state of the first electric motor, and (c) a second electric motor connected to a power transmitting path between the electrically controlled differential portion and a drive wheel of a vehicle. JP-2005-264762A discloses an example of a control apparatus for such a vehicular drive system. The control apparatus disclosed in this publication is configured to rapidly raise the operating speed of the engine to a value permitting ignition of the engine, by operating the first electric motor and the second electric motor in the same direction, for thereby starting the engine.
In the hybrid-type vehicular drive system as disclosed in the above-identified publication, a switching portion in the form of a clutch device is engaged to switch the above-indicated power transmitting path from the power cut-off state to the power transmitting state upon a shift lever is operated from a neutral position to a forward-drive position while the vehicle is moved down backwards on a downhill roadway, for example, with the shift lever placed in a rear-drive position. An engaging action of the clutch device causes drops of the rotating speed of an output shaft of the differential mechanism and an operating speed of the second electric motor connected to the output shaft of the differential mechanism. Consequently, an inertia torque is generated due to a differential function of the differential mechanism, so as to lower the operating speed of the engine, so that the engine is slightly rotated in the negative direction, giving rise to deterioration of the durability of the engine.